Thermostatic fire detector



Oct. 14, 1947. J. H. DERBY 2,428,338

THERMOSTATIC FIRE DETECTOR Filed Sept. so, 1943 BY. I Q 5% ATTORNEY.

Patented Oct. 14, 1947 UNITED STATES PATENT. OFFICE 2,428,838TuEaMos'rAnc FIRE na'rac'roa John 11. Derby, sema ie, N. Y.

Application September 80, 1943, Serial No. 504,407

6 Claims.

This invention relates to thermally operated circuit controlling devicesand particularly to thermally operated circuit controlling devices whichcontrol the circuits of fire'alarm or fire control systems.

Thermally operated circuit controlling devices for fire alarm or firecontrol systems are usually of one of two types now in general use, thatis, they operate usually either upon a rise of temperature above apredetermined critical temperature for which the device is calibrated orthey operate when the rise in temperature exceeds a certain minimum rateper unit of time. Each type of device has advantages for certain uses.For example, the rate of rise thermostatic circuit control device forfire alarm or fire control systems is more sensitive to fires that startsuddenly and may thus give an alarm for an incipient fire "before theroom temperature would reach the critical point for the operation of afixed temperature circuit control device. The rate of rise circuitcontrolling devices, however, have a disadvantage in that theyfrequently give false fire alarms for rapid temperature rises in thecontrolled space which exceed the calibrated rate but which areperfectly harmless. Such rises may be caused by the opening of a doorbetween a highly heated room and one not so heated, by the uncovering ofa kettle in which a liquid is boiling, by.release of a steam safetyvalve and by the occurrence of various other events which are perfectlyharmless in themselves but which bring about the critical rate of riseoftemperature necessary to operate the circuit control devices.

To insure ideal protection, therefore, it is advantageous to combine therate of rise thermostatic circuit controlling device with the fixedtemperature circuit controlling device thereby not only giving warningof fires producing quick temperature rises below the criticaltemperature of the fixed temperature thermostat but also, through thefixed temperature thermostat, giving a warning where the fire is of sucha nature that the temperature rise to the danger point is below thecalibrated rate for the rate of rise element.

A general object of the present invention is to provide a compact,simple, efficient and substantially dustand corrosion-proof combinedrate of rise and fixed temperature circuit controlling device whichcombines all of the advantages of each of the aforementioned types ofdevices and which can be installed in all kinds of locations,

where fire alarm and fire control thermostatic systems are desirablewith assurance that it will operate when needed.

A particular object of the invention is to provide a device of this sortin which a single circuit closer may be operated either ,by the rate ofrise operating mechanism or by the fixed temperature thermostaticmechanism or by both.

Another object of the invention is to provide for the enclosure of allof the operating parts of the device within a housing which not only issubstantially dustand moisture-proof, but a part of which also serves asthe expansion chamber for the rate of rise mechanism, said housing alsoenclosing therein a dash pot chamber for preventing the sending in ofalarms for fiash rises of temperature, exceeding the calibrated rate,but not representing an incipient fire.

An important feature of the invention is the provision of means forvarying the calibration of each of the circuit control devices of thecombined unit from the outside of the unit, without having todisassemble the unit, the said adjusting means being adapted to besealed in their calibrated adjustments.

Other objects and important features of the invention will appear whenthe following description and claims are considered in connection withthe accompanying drawings in which the figure is a transverse sectionthrough a combined rate of rise and fixed temperature circuitcontrolling device embodying the present invention, the device beingshown in the position in which it is attached to the ceiling or upperpart of the space to be protected against fires.

In the illustrative embodiment of the invention, the molded base 2, ofBakelite or other suitable insulating material, has a depending threadedflange 4 on which is screwed a clamping ring 6, which may also be madeof Bakelite or other suitable insulating material, although notnecessarily so.

The. hemispherical air chamber casing I, which may be formed of copperor brass or other high heat conducting material and which may be paintedblack to insure more rapid heat absorption, is provided with a reentrantfiange portion ill between the upper and lower parts of which themarginal edges of both the diaphragm l2 and its backing plate i3 areconfined. Itwill be seen that when the ring 6 is screwed up intoclamping relation to the flange ill of the air chamber 8, it willsqueeze the marginal edge of the diaphragm i2 and the marginal edge ofits backing plate l3 between the upper and lower parts of the flange i0and thus hold them tightly against slippage under the action of the airexpanding in the chamber 8. The diaphragm I2 is preferably corrugated asshown and is cut out in the center to receive the threaded boss I on theupper clamping plate IS, the boss' ll having an unthreaded portionbetween its threaded end and. the clamping plate IE to receive a lowerclamping plate I! fitting about the unthreaded portion. The inner edgeof the diaphragm I2 is clamped between the upper and lower plates [6 andI8 and is secured in its clamped position by a clamping screw 20 screwedon to the threaded end of the cylindrical boss l4.

The upper clamping plate l6 carries at its center a con-tact member 22,which may have a stem screwed into a threaded opening in the clampingplate l6 or which may otherwise be secured thereto, the plates l6 and I8being made preferably of some conductive and not readily corrodiblematerial such as copper, brass or bronze an he contact member 22 beingmade preferably of some non-corrodible metal such as silver.

To limit the movement of the diaphragm l2 under the action of the airexpanding in the casing 8, the annular backing plate [3 is provided onthe upper side of the diaphragm l2, this backing plate I3 having anoffset flange portion which is also clamped between the upper and lowerparts of the flange I 01. the air chamber 8, together with the marginaledge of the diaphragm [2, as hereinabove described. The contact member22 has electrical connection to the one side of the electric circuit tobe controlled by the operation of the diaphragm l2, under the action ofthe air expanding in the casing 8, by means of a terminal 28 having awire clamping screw 30 threaded therein, said terminal having an offsetpart 32 clamped in the Bakelite base 2 by a screw 34 threaded thereinto,said screw extending through the base 2 and having a conical end whichengages the upper face of the diaphragm backing plate l3. It will beseen, therefore, that electrical connection is made between the terminal28 and the silver contact member 22 through the screw 34, the backingplate i3 and the diaphragm i2 which is clamped against the backing plate[3, between the upper and lower parts of the flange ID of the casing 8,by the clamping ring 6, the diaphragm I2 being in electrical connectionwith the contact member 22 through the upper clamping plate 16.

It will further be seen that through the screw 34 and the diaphragmbacking plate l3, electrical connection is made between the terminal 28and the metallic casing 8. The thermostatic circuit closing means whichis mounted on the metal casing v8 of the air chamber will now bedescribed. The fixed temperature thermostatic circuit controlling meanscomprises a bi-metal strip 36 attached to the metal air chamber casing 8at 38, preferably both by rivets and by solder to insure good permanentelectrical and heat conducting connection to the casing 8. The bimetalstrip 36 is curved as shown so that when it expands and tends tostraighten, the contact point 40 on the upper side of the curve iscaused to press with considerable force against the lower face of theboss 14 on the upper clamping member I6, thus tending to force thediaphragm upwardly and with it the silver contact 22. When the silvercontact 22 is forced upwardly a suiilcient distance, however, either byexpansion of the air in the chamber 8 or by the tendency of the bi-metaltaq screw 42 is provided with a kerf 50 to re- The terminal 46, like theterminal 28, is

ceive a screw driver to facilitate calibrating the control device andthat this upper end of the screw is seated in a recess in the upper partof the clamping screw 44 so that, after the calibration has beeneffected, sealing wax or other suitable sealing means 62 may be placedover the upper end of the contact screw 42 and, if desired, confinedtherein by means of another short screw 54 screwed into the upper end ofthe said recess in the clamp screw 44. Calibration of the action of thebi-metal strip 36, that is, calibration of the fixed temperaturethermostatic circuit controlling means, ma be effected by means of acalibrating screw 56, threaded through a screw case or holder 58 havinga flange on the inside of the air casing 8 and preferably soldered tothe casing 8 to secure an air-tight joint. The adjusting or calibratingscrew 56 has its keri 62 located at the bottom of a recess in the casingor holder 68 so that it also, when properly calibrated, may be sealedagainst access by sealing wax 64 or by any other suitable or morepermanent sealing means.

It will be noted that, when the parts are in the position shown in thedrawings, all of the contacts are enclosed within a casing comprising,as a whole, the base 2 of insulating material, the clamping ring 6 andthe metal air chamber casing 8. It will further be seen that thediaphragm l2 and the clamping plates [6 and 18 carried thereby dividethis enclosure into two chambers 66 and 68. To prevent gradual expansionof the air in the lower chamber 66 from moving the contact 22 intoengagement with the contact 42, a

leak or vent is provided in the diaphragm l2 through which the slowlyexpanding air can gradually leak. As herein shown, this leak or ventcomprises a tube 10, preferably oi non-corrodible metal, cemented intoan opening through the upper and lower clamping plates [5 and I8, Asherein shown, the tube 10 has in its lower end an opening 12, aboutone-half the diameter of the opening 14 in its upper end. The tubepreferably has therein a lug 16 of suitable porous material such, forexample, as balsa wood or other porous compressible wood. The rate offlow of the air leaking through the plug 16 may be varied by varying theinitial compression of the balsa or other wood. The function of thisleak is partly to determine the calibration of the rate of rise circuitcontrolling device. In order to prevent some false alarms, a secondcalibrated leak or vent is provided in the upper chamber 68. This leakor vent comprises simply a plug of balsa wood or other suitable material18 in an opening 80 in the Bakelite base 2, this leak being socallbrated that it will pass air therethrough faster pot action of theair in the chamber 68 as it is driven through the leak or plug 18. Bothleaks, of course, permit the return of the diaphragm l2 to its normalposition under the action of gravity, this return preferably beingfacilitated by making the clamping plates l6 and iii of substantialdimensions and of suillcient weight to tend to carry the diaphragmquickly back to its normal inoperative position.

It will be seen that the balsa wood plug 18 in the opening has a furtherfunction in that it protects the chamber 68 from the ingress of dust,moisture 01' other vapors and thus protects the inside plug 16 frombecoming clogged.

Opening upon the upper side of the Bakelite base 2, the plug or leak 18is itself also somewhat protected from dust by the outlet box, withinwhich it is preferably enclosed. It is believed that the use of balsawood for an air leak of this type is novel.

From the foregoing description, it will be seen that the inventionherein disclosed provides a combined rate of rise and fixed temperaturethermostatic unit for fire. alarm and fire control purposes having manyadvantages over previous devices and that it is simple to make, compactand inconspicuous and also substantially dustand moisture-proof. It willfurther be seen that it combines the best features both of the rate ofrise and of the fixed temperature circuit control devices in a unit inwhich there is only one pair of circuit closing contacts.

It is to be understood of course, that the embodiment of the inventionherein shown is illustrative only andthat many other embodiments may bemade within the spirit of the invention and the scope of the claims.

I claim:

1. Ina thermostatic circuit controlling device, the combination with ahollow casing of good heat conducting material, a diaphragm forming withsaid casing an expansion chamber for the diaphragm-operating fluid, saidchamber being provided in a wall thereof with a restricted pressureequalizing vent for gradual temperature changes, and circuit-closingmeans comprising a member movable by said diaphragm, intocircult-closing position upon expansion of the fluid'- in said chamberat a rate in excess of the capacity of said vent to effect equalization,of a bi-metallic thermostat enclosed within said expansion chamber,connected to said casing at one end only and bent in an arch-like curve,with the metal having the higher coemcient of expansion on the inside ofsaid curve, between said casing and the diaphragm in such manner thatits free end bears against the diaphragm and the opposite side of thearch has its bearing on the casing, said bimetallic thermostatbeing soadjusted that its free end exerts pressure on said diaphragm suflicientto effect a circuit closing movement thereof when the temperature insaid chamber reaches a selected critical point above normal and returnsto its potentially operative position when the temperature in saidchamber again falls below said critical point.

2. Thermostatig,circ11it-closing means according to claim 1 in which thecasing, the diaphragm and the bi-metallic thermostat are all inelectrically conductive relation to each other and to one-side of thecircuit-closing means.

3. A thermostatic circuit controlling device according to claim 1 inwhich the casing bearing of the bi-metallic arch is adjustable towardand away from the diaphragm to provide for variation of the criticaltemperature at which the bimetallic thermostat operates to close thecircuit.

4. Athermostatic circuit controlling devicei according to claim 1 inwhich acritical temos perature adjusting bearing for the casing side ofthe bi-metallic arch has an extension to the outside of said casing bymeans of which such adjustment may be made.

5. In a thermostatic circuit controlling device. the combination with ahollow casing of good heat conducting material, a diaphragm forming withsaid casing an expansion chamber for the diaphragm-operating fluid. saidchamber being provided in a wall thereof with a restricted pressureequalizing vent for gradual temperature changes, and circuit-closingmeans comprising a member movable by said diaphragm into circuit-closingposition upon expansion of the fluid in said chamber at a rate in excessof the capacity of said vent to effect equalization, of a bi-metallicthermostat enclosed within said expansion chamber, connected to saidcasing at one end only and having its free end arranged and ad- Justedto exert pressure on said diaphragm sufficient to effect circuit closingmovement thereof when the temperature in said chamber reaches a selectedcritical point above normal and to return automatically to itspotentially operative position when the temperature again falls belowsaid critical point, and means for varying the critical setting of thebi-metallic thermostat, said means being arranged to be accessible fromoutside the casing without disassembling thereof or removal of thethermostatic circuit controlling device from its operative location.

6. In a thermostatic circuit controlling device, the combination with ahollowcasing of good heat conducting material, a diaphragm forming withsaid casing an expansion chamber for the diaphragm-operating fiuid, saidchamber being provided in a wall thereof with a restricted pressureequalizing vent for gradual temperature changes, and circuit-closingmeans comprising a member movable by said diaphragm into circuit-closingposition upon expansion of the fluid automatically to its potentiallyoperative position when the temperature again falls below said criticedpoint and an insulating base provided with a ependingfiange to which thecasing and diaphragm are clamped, said diaphragm forming with saidflange a second substantially dustproof chamber into which the chambervent discharges and in which the circuit closing means is located, aless restricted screened vent being also provided in the outside wall ofsaid second chamber. the relative sizes of the chamber vent and theoutside wall vent being such as to cause the fiuid in said secondchamber to effect a dashpot retardation of the movement of saiddiaphragm under excessive rates of expansion of the fiuid in the firstmentioned chamber.

JOHN H. DERBY.

anraaancas crran The. following references are of record in the file ofthis patent:

UNITED STATES PATENTS Great Britain Aug. 18, 1943

